The invention relates to virtual machine migration, and more particularly to migrating virtual machines across sites.
In order to improve the security and continuity of data storage, more and more companies create their data center at different locations sites to prevent disaster or adjust and balance the load. On the other hand, along with the development of virtualization technique, many data centers use virtual machines to realize the management of data. In many cases such as maintaining sites, adjusting the power, balancing the load between sites and so on, it may be necessary to move the loaded virtual machines across sites, i.e., to migrate virtual machines from one physical system to another different physical system. However, migrating virtual machines without influencing their applications and services is a common concern.
Most companies who provide host virtualization have their special virtual machine migration tools. For example, some current tools have a virtual machine migration function, which can move a running virtual machine to a different physical system without encountering any down-time. However, the current migration tools both require a centralized shared storage, such as SAN (storage area network), NAS (network-attached storage) and so on, between the source and the target physical system. Such a requirement limits the virtual machine migration to be executed within the same site, and thus makes the system unable to execute the migration across sites.
Furthermore, in order to overcome the above limitation, computing facilities have implemented various methods for virtual machine migration across sites. One solution realizes virtual machine migration by firstly suspending and mirroring a virtual machine to an image, then copying it through network, and finally resuming it in another computer. However, this is a stop-and-copy process, which obviously interrupts the running of the virtual machine, and causes its applications or services to halt or timeout. Another solution proposes to set up optical paths dynamically between hosts, via which a virtual machine can be migrated from the source site to the target site. But this solution needs to install a tunable controlling agent on each virtual machine, and requires a Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), or Dense Wavelength Division Multiplexing (DWDM) connection between hosts to copy data on the memory and disks. It is understood that each application or service is expected to still run during migration, therefore data accessing and changing still happen on disks. When the data changing rate on disks is higher than the network copying rate, a part of data cannot be copied to the target site, which causes data loss. Therefore, this solution does not address the data consistency problem, which is disadvantageous for the security of virtual machine migration.